Roll src/third_party/skia/ 6536ae590..a00980e58 (2 commits).
Roll src/third_party/skia/ 6536ae590..a00980e58 (2 commits).

https://chromium.googlesource.com/skia.git/+log/6536ae590e38..a00980e58037

$ git log 6536ae590..a00980e58 --date=short --no-merges --format='%ad %ae %s'
2016-05-02 jvanverth Make sure that Vulkan debug callback ptr is non-null.
2016-05-02 bsalomon When filling nested rect path check for empty inner and empty outer rects

CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
TBR=jvanverth@google.com

Review-Url: https://codereview.chromium.org/1938863003
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#391076}

axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk